Voltage-limiting arc interrupter



April 19, 1949. R. R. PITTMAN 2,467,443

VOLTAGE-LIMITING ARC INTERRUPTER Filed Feb. 19, 1943 2 SheetsSheet 1 2 Sheets-Sheet 2 Filed Feb. 19, 1948 INVENTOR. 4! Q Patented Apr. 19, 1949 UNITED STATES PATENT OFFICE Claims.

This invention relates generally to lightning discharge devices of a character adapted for use with electrical circuits for limiting the voltage rise of a conductor by discharging abnormal or superimposed energy to ground and preventing the passage of energy through the discharge device upon attainment of normal electrical conditions.

The present invention is an improvement on the construction described in Patent No. 2,164,720, issued to Ralph R. Pittman, and dated July 4, 1939, and a substitute for abandoned application Serial No. 580,986, In the above-specified patent there is described a tube-filler type of are extinguishing device in which an arc originates along an abutment line between a tube and a filler eccentrically located therein and the arc is subsequently bodily moved and elongated until extinguished, this functioning being the result of a construction in which the originated arc is initiated across a gap one electrode of which is a conducting member extending upwardly along the abutment line. This is an effective device, despite the fact that the construction is such that peripheral arc movement around the filler cannot be predetermined as to direction clockwise or counterclockwise, and further is substantially limited to M2 the length of the periphery of the filler, or from the originating arc path of greatest restriction to the final or extinguishing path of least restriction. This construction is improved by my invention herein by retaining the desirable features of arc movement and are elongation, and at the same time making possible the initiation of the are along a path less restricted than the path along the abutment line, for the reason that lightning current discharged along the path of maximum restriction results in maximum accompanying impact, which must be resisted by providing high strength members.

An object of my invention is to provide, in an arc interrupter embodying an eccentrically located filler within a tube, a construction in which sparkover is caused to occur over a predetermined path which is less restricted than that along the abutment line. An additional object is to provide in such a device means for causing arc movement and accompanying elongation to occur over a predetermined path peripherally of the filler. A further object is to provide a construction in which are movement around the filler may under certain conditions exceed one-half the peripheral length of the filler.

In general, the arc interrupter of my invention comprises a tubular insulator containing a filler of insulating material so mounted that the filler abuts the insulator along a longitudinal line on the inner wall of the tubular insulator, and conducting members so associated with the filler and insulator as to cause breakdown or sparkover to occur over a predetermined longitudinal path in the space between the filler and the tubular insulator. As the gas generated by the arc moves in a direction away from the abutment line around the filler to a suitably disposed vent, the arc is blown from its originating position and concurrently lengthened, and is thereby extinguished. By means of the construction of my invention, the direction of arc movement may be predetermined, the arc may be caused to originate in any chosen degree of restriction of path, and the extent of peripheral arc movement appreciably increased over that occurring in constructions disclosed in the prior art.

An important advantage of my arc interrupter is the fact that both surge capacity and follow current interrupting ability may be readily adjusted within a substantial range by simply altering the position of the conducting member forming the initiating electrode which causes sparkover to occur over a predetermined path.

My arc interrupter is particularly advantageous for use in a construction in which it is not desired to allow the arc to remain in one position until sufficient material is volatilized from the bounding walls to cause extinguishment, but rather to cause arc movement over cool surfaces until the arc is extinguished. In the absence of arc movement, an arc playing against a hard fiber surface such as is suitable for the filler and tube of my invention, evolves gases which are largely hydrogen and oxides of carbon, which are the result of destructive distillation, and evidenced by grooving and erosion. With rapid arc movement, the heat of the are does not have time to penetrate much below the surface, water vapor is evolved to cause the desired arc movement to extinction, and replacing moisture subsequently reabsorbed from the atmosphere, thus eliminating the erosion which accompanies the operation of many types of expulsion devices. It will be apparent from the above considerations that a construction in which are movement is greatest for a given size of device is most advantageous.

These and other objects and advantages will be more apparent from the following description of the accompanying drawing which illustrates a specific embodiment of my invention, and the scope of the invention will be indicated by the appended claims.

In the drawing: Fig. 1 is a longitudinal view of an arc interrupter constructed according to the principles of my invention, shown partly in section; Fig. 2 is a section along the line 11-11 of Fig. 1; and Fig. 3 is a view of the lower end of the lower end of the arc interrupter. In addition to the several views of the interrupter, Fig. 4 has been included to illustrate a fragmentary development of the inner bounding surface of the arc space, showing successive positions taken by an imaginary are from inception to extinguishment.

The are interrupter illustrated in Figs. 1, 2, and 3 comprises the longitudinally extending tube of insulating material i8, to the upper end of which is suitably fastened, as by screw threads, the metal cap it, the latter providing both a closure for the upper end of the tube and a conducting electrode extending over the arc chamber from the upper conductin terminal member l2. The leakage gap indicated at the numeral II, in accordance with usual practice, is interposed between the terminal member l2 and the conductor ill, the voltage of which it may be desired to limit to some predetermined amount. The conducting cap 20 threadedly engages the lower end of the tube I8, and for reasons later to appear, is provided with the vent 2!, the latter extending only partially around and in registration with the inner periphery of the tube It. The lower conducting terminal member 22 extends upwardly in threaded engagement through the lower cap 20, and downwardly therefrom, and to the downwardly extended portion the mountin bracket 26 (partially shown), and the conductor 25 are fastened, respectively by means of the terminal nuts 23 and 24. As shown in Fig. 1, the arc interrupter is in position to discharge excessive voltages appearing between the conductor l and the conductor 25.

The filler l5, of insulating material, extends longitudinally in and is contained by the tube [8. The respective ends of the filler l5 are provided with inwardly extending recesses into which are respectively extended the upper terminal member 12 and the lower terminal member 22, the resilient bushing M, of live rubber or other suitable material, being interposed between the outer surface of the downwardly extended portion of the terminal member 12 and the wall of the recess at the upper end of the filler l5, and the resilient bushing H3, at the lower end of the filler l 5, is similarly arranged with respect to the terminal member 22.

The members just described are so arranged that the filler i5 is held in lateral abutting engagement with the inner surface of the tube It! along an abutment line, as shown in Fig. 2, and the unoccupied space between the tube and filler provides the arc space of the construction. As may be noted by inspection of Fig. 2, the longitudinally extending path of minimum divergence of the inner wall of the tube I8 with repect to the outer surface of the filler I5 is along the abutment line, and that of maximum divergence is displaced peripherally from the abutment line by an angle greater than 180 degrees. To establish a predetermined sparkover path through the device, the initiating electrode constituted by the conducting members It and i1 is provided. The member l6 extends upwardly through the filler 15 toward and in spaced relation with the upper electrode l3, contacting at its lower end the lower terminal member 22, and at its upper end the inner end of the radially extending member H. The outer end of the member [6 terminates at the outer surface of the filler l5, at a point ofiset from the abutment line, peripherally be tween the paths of minimum and maximum divergence, and in longitudinal spaced relationship with the upper electrode l3. The spacing of the electrode I! from the upper electrode 13 is the shortest distance between the conducting elements associated respectively with the upper and lower ends of the tube l8, and is thereby established as the weakest electrical path over which sparkover is caused to occur. Both the filler l5 and the tube l8 are preferably of some material having resistance to heat, and ability to evolve cooling gas in the presence of an arc. Hard fiber is the best material I have so far discovered for this purpose.

From an inspection of Fig. 2 it will be apparent that the path of maximum divergence is peripherally displaced more than 180 degrees from both the electrode I! and the line of abutment by forming the peripheral surface of the filler in the form of a spiral. This contruction illustrates, as compared with other constructions known to me, the much longer peripheral distance which an arc may be caused to traverse, in a given size structure, by the use of my invention.

The operation of my invention may be clearly explained in connection with Fig. 4. When a predetermined difierence of potential between the respective normally insulated conducting members l3 and '20 occurs, sparkover is caused over the weakest electrical path, this sparkover being indicated by the longitudinally extending line designated by the letter a, and extending from the initiating electrode I l and the point 28 on the upper electrode l3. Gas evolution immediately accompanies the discharge. The abutment line prevents movement of gas toward the abutment line, and gas movement occurs in the direction of the arrows of Fig. 5. The are is carried along with the gas through the successive positions indicated at b, c, d, and e. At the latter position, because of approach to theabutment line from the opposite direction, the gas is caused to move substantially longitudinally through the arc to the vent 2|, resulting in maximum contact of the gas with the are, which is a condition for eiiective extinguishment. The desired movement of the gas is facilitated by positioning the vent longitudinally under the path of least restriction, as illustrated.

It will be apparent that the impact caused by large discharges of lightning current is cushioned in my invention by causing sparkover to occur through the air space between the insulating elements, and that the discharge tends to roll the filler along the inner surface of the tube, rather than blasting it directly away from the abutment line. It may be further noted that great flexibility of design is possible through the principles exemplified by my invention, by adjustment of the position of the sparkover path and of that of the vent.

In the practical application of my invention, best results are obtained by using larger diameters of tube and filler than are usually found in common practice. Usual filler diameters are of the order of one-half of one inch. Such diameters are insufficient to provide the necessary peripheral length of arc travel to obtain best operation and avoid substantial erosion. In practice, elongation of arc with 1% inches of peripheral movement, using {-5- inch fillers and 4' inch tubes, with a length adjusted to the voltage to be interrupted, has given fair results. Much better results have been obtained using fillers of about 1 inch diameter in l-f inch tubes, thus doubling the peripheral arc movement.

Many modifications and changes in my inven-,

tion will be apparent from the description herein, and it is intended that this description will be regarded as illustrative, rather than limiting.

I claim as my invention:

1. A voltage-limiting are interrupter comprising insulating members including a longitudinally extending tube vented at one end thereof and a filler therein partially closing the bore of said tube, conducting terminals mounted at the respective ends of said tube, means holding said filler in lateral abutting relation with the internal surface of said tube along a single longitudinally extending abutment line to provide between the inner surface of said tube and the outer surface of said filler a single undivided curved arc space which extends entirely around said filler, the distance between the outer surface of said filler and the inner surface of said tube continuously increasing peripherally from said abutment line to a line parallel thereto and peripherally spaced more than 180 degrees therefrom, and structural means for causing sparkover to occur longitudinally along said filler within said are space over a predetermined line between said abutment line and said peripherally spaced line, said structural means including conducting electrodes mounted in longitudinally spaced normally insulated relationship along said are space and so coordinated with said insulating members that said predetermined line is the weakest electrical path within said tube between said terminals.

2. A voltage-limiting arc interrupter comprising insulating members including a longitudinally extending tube vented at one end thereof and a filler therein, said filler having a smaller crosssectional area than that of the bore of said tube, conducting terminals mounted at the respective ends of said tube, means holding said filler in lateral abutting relation with the internal surface of said tube to provide therebetween a. single undivided curved arc space which extends longitudinally over the length of said filler and peripherally more than one-half the distance around said filler, the divergence of the outer surface of said filler with respect to the inner surface of said tube continuously increasing peripherally from said abutment line to a peripherally spaced line parallel thereto and more than 180 degrees therefrom, and structural means for causing sparkover to occur longitudinally along said filler within said are space over a predetermined line between said abutment line and said peripherally spaced line, said structural means including conducting electrodes mounted in longitudinally spaced normally insulated relationship along said are space and so related to said insulating membars that said predetermined line is the weakest electrical path within said tube between said terminals.

3. A voltage-limiting arc interrupter comprising insulating members including a longitudinally extending tube vented at only one end thereof and a filler contained by said tube, said filler having a smaller cross-sectional area than that of the bore of said tube, conducting terminals mounted at the respective ends of said tube, means holding said filler in lateral abutting relation with the internal surface of said tube to provide therebetween a single undivided curved are space which extends longitudinally over the length of said filler and peripherally more than one-half the distance around said filler, the divergence of the outer surface of said filler with respect to the inner surface of said tube continuously increasing peripherally from said abutment line to a peripherally spaced line parallel thereto and more than degrees therefrom, and structural means for causing sparkover to occur longitudinally along said filler within said are space over a predetermined line between said abutment line and said peripherally spaced line, said struc tural means including conducting electrodes mounted in longitudinally spaced normally insulated relationship along said are space, one of said electrodes extending inwardly into said are space from that conducting terminal at the vented end of said tube to a point at one end of said predetermined line whereby the latter is established as the weakest electrical path between said terminals.

4. A voltage-limiting arc interrupter comprising insulating members which evolve gas in the presence of an arc, said insulating members including a longitudinally extending tube and a filler therein, said filler having a smaller cross-sectional area than that of the bore of said tube, conducting terminals mounted at the respective ends of said tube, means holding said filler in lateral abutting engagement with the internal surface of said tube to provide therebetween a single undivided arc space which extends longitudinally over the length of said filler and peripherally more than onehalf the distance around said filler, the divergence of the outer surface of said filler with respect to the inner surface of said tube continuously increasing peripherally from a minimum at said abutment line to a maximum at a peripherally spaced path parallel thereto and more than 180 degrees therefrom, and structural means for causing sparkover to occur longitudinally along said filler within said arc space along a predetermined line between said abutment line and said peripherally spaced path, said structural means including conducting electrodes mounted in longitudinally spaced normally insulated relationship along said are space and so related to said insulating members that said predetermined line is the weakest electrical path between said terminals, and a vent opening directly into that position of said are space having maximum divergence.

5. A voltage-limiting arc interrupter comprising insulating members which evolve gas when subjected to the heat of an arc, said insulating members including a longitudinally extending tube and a filler contained by said tube, said filler having a smaller cross-sectional area than that of the bore of said tube, conducting terminals mounted at the respective ends of said tube, means holding said filler in lateral abutting relation with the internal surface of said tube to provide therebetween a single undivided arc space which extends along said filler and peripherally more than one-half the distance around said filler, the divergence of the outer surface of said filler with respect to the inner surface of said tube continuously increasing peripherally from a minimum along said abutment line to a maximum along a parallel path peripherally spaced more than 180 degrees therefrom, said tube being closed at one end and provided with a vent at the other end, said vent being located in longitudinal alignment with that portion of said arc 7 space having maximumdivergence,z and structural means for causing sparkover. to occur longitudinally along said fillerwithin said arc space over a predetermined line between the line of minimum divergenceand'theperipherally spaced path of maximum divergence, said structural means including conducting electrodes mounted in longitudinally spaced normally insulated relationship along said are space, one of said electrodes extending inwardlyintosaid arc space from thatconducting terminal at the vented end of said tube to a point at one end of said predetermined line whereby the latter is established as the weakest electrical path between said terminals.

RALPH R. PITTMAN.

No references cited. 

